The long term objectives are to understand the relationship of pregavid maternal lipid metabolism and maternal metabolic adaptations during pregnancy at the system and cellular level. The specific aims of this proposal are to: evaluate the longitudinal changes in maternal insulin sensitivity as it relates to maternal lipid metabolism and fat accretion in lean and obese women with normal glucose tolerance and gestational diabetes; evaluate the alterations in maternal lipid metabolism in late pregnancy in relationship to neonatal body composition; and, identify the cellular mechanisms underlying decreased insulin sensitivity in adipose tissue during late gestation in normal glucose tolerance and gestational diabetes.